Ancient Chinese Astronomy: New insights from old information

Ancient Chinese Eclipse Predictions

The Chinese were also careful to record eclipses of the Sun – a portent of doom that would directly affect the Emperor or his family. “There was a total eclipse in 181 BC,” says Stephenson, “and the Emperor’s dowager was really alarmed by it: she died two years later.”

An eclipse features in the earliest astronomical record in the world, from the Chinese city of Anyang. Around 3000 years ago, a diviner inscribed a question on an oracle bone – a polished shard of animal bone: “Diviner Ge asks if the following day will be sunny or not.” He pushed in a red-hot needle, and interpreted the ensuing cracks.

Twenty-four hours later, the diviner inscribed the actual answer to the question. In this case, something rudely interrupted the sunshine: “Three flames ate the Sun, and big stars were seen.”

This is clearly an account of a total solar eclipse. The “flames” were the Sun’s outer atmosphere, the corona, with the brighter stars and planets becoming visible during the darkness of totality.

To astronomers’ eternal gratitude, Diviner Ge recorded that the eclipse fell on the 52nd day of the 60-day lunar month. In 1989, NASA researchers calculated when a total solar eclipse would have been seen in China on the 52nd day of any month. The only date that fits is 5 June 1302 BC – making this eclipse the most ancient exactly dated astronomical event.

This eclipse isn’t important only as a record-breaker. It reveals new information about the Earth’s rotation. Astronomers know that our day is gradually getting longer, due to the influence of the Moon’s gravity – that’s why we have to occasionally insert “leap seconds” to our clocks. But the rate of slowing isn’t constant.

By studying exactly where eclipses have been seen over the past millennia, Stephenson has tracked the variation in the Earth’s rotation rate. As well as the Moon’s influence, he has to invoke minute changes in the Earth’s shape as the surface bounces back from the weight of ice sheets that burdened northern lands during the last Ice Age: “especially in the area around the Gulf of Bothnia, the land’s still rising at quite a rate.”

These results are showing – in a way the ancient Chinese could never have predicted – that their scrutiny of the heavens has indeed been mirrored in the planet under their feet!

Read more about humankind’s quest to understand the heavens, from ancient times to the 21st century, in The History of Astronomy by Heather Couper and Nigel Henbest (Cassell Illustrated)!

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An interactive tour of Chinese Astronomy
http://www.dragonskies.org/dragon_skies.html

Comprehensive coverage of Chinese astronomy
http://www.chinapage.com/astronomy/astronomy.html